The present invention relates to a structure of a gas laser tube, and more particularly to a structure of an exhausting section of a gas laser tube.
In recent years, the fields of application He-Ne gas laser tubes have been more and more expanded, and a large of demand is expected, especially in point of sales (POS), information processing systems, video discs, etc. Therefore, laser tubes having a structure suitable for mass production and of low cost are required. Particularly desired are those laser tubes which are as simple as possible in structure and thus necessitate no special work for manufacture and which have a reduced number of manufacturing steps.
U.S. Pat. No. 4,081,762 discloses a structure of a gas laser tube which satisfies such requirements to a certain extent. In this gas laser tube, metal caps are provided at the opposite ends of a vacuum envelope disposed coaxially with a laser capillary, and at the central portions of these metal caps are respectively mounted via support members mirrors forming a resonator. In addition, an exhaust tube or vent is attached to one of the metal caps adjacent to the mirror support member. The exhaust tube is sealed off after evacuation. However, in this known gas laser tube, the exhaust tube is provided separately from the mirror support member, so that the work of fixing and sealing the mirror and the work of sealing the exhaust tube must be performed separately. Thus, this known gas laser tube has the disadvantage that the number of steps for manufacture is too large.
Another prior art internal mirror type He-Ne gas laser tube is shown in FIG. 1, which is disclosed in, e.g., U.S. Pat. No. 4,012,214. In this laser tube, a laser medium is generated by electric discharge within a laser capillary by applying an appropriate voltage between an anode electrode 1 and a cathode electrode 2. Laser light is taken out in the direction of the arrow by the action of an optical resonator composed of circular mirrors 7 and 8 which are air-tightly secured by glass solder 6 to cylindrical metallic members 4 and 5, respectively, at the opposite ends of the laser tube. A hollow metallic member 9 serves as means for adjusting alignment of the mirror axes. Exhaust of unnecessary gas from this laser tube is performed through an exhaust tube 11 planted at the shoulder portion of an envelope 10. However, connection to an exhaust apparatus and sealing off of the exhaust tube 11 depend entirely upon manual work employing a gas burner, which requires skilled operations, resulting in a increased costs due both to poor workability and limited workers. Since an exhaust tube made of glass is used and it is located at an inconvenient position, the yield of the coupling of the exhaust tube to an envelope is poor, and this is another cause of increased cost. In addition, breaking and cracks often occur at the exhaust tube itself.